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Evidence of Ancient Martian Rivers

This picture from NASA's Mars Global Surveyor could help settle a decades-long debate about whether the planet had long-lasting rivers instead of just brief, intense floods. The image of the delta-like fan shows eroded ancient deposits of transported sediment long since hardened into interweaving, curved ridges of layered rock. Scientists interpret some of the curves as traces of ancient "meanders" made in a sedimentary fan as flowing water changed its course over time.

"Meanders are key, unequivocal evidence that some valleys on early Mars held persistent flows of water over considerable periods of time," said Dr. Michael Malin of Malin Space Science Systems, San Diego, which supplied and operates the spacecraft's Mars Orbiter Camera.Photo Credit: NASA/JPL/Malin Space Science Systems